This invention relates to the fabrication of composite materials, and, more particularly, to the fabrication of composite materials using matrix materials that are difficult to machine.
A composite material is formed from two or more constituent materials that retain their physical form and identity in the composite material, as distinct from an alloy wherein the constituents lose their physical form and identity. The composite material can have various types of structure, but one commercially important type of composite material consists of elongated reinforcement fibers of one material embedded in a matrix of another material. The matrix material holds the fibers in the desired orientation, and protects the fibers from damage that may weaken the fibers. The interfaces between the fibers and the matrix can be controlled to achieve particular properties in the composite material.
The marty possible combinations of fiber type, fiber orientation, matrix type, and interfacial characteristics permit the properties of the composite material to be tailored to achieve specific properties and for particular design applications. As a result, composite materials have become increasingly important and widely used in products, particularly those that must achieve high performance standards combined with low material weight.
One of the important possibilities created by the use of composite materials is the improvement of materials that otherwise are difficult to use in applications by reducing the adverse effect of some undesirable property. For example, in the past it has been conventional design practice to use materials that are relatively ductile, In order to achieve fracture toughness in the final product. However, as products are developed for use at ever-higher temperatures, it is found that the only materials which can practically provide the required high-temperature strength and environmental stability are intermetallic compounds and ceramics which exhibit relatively low elongations to failure, and therefore may have inherently low fracture toughnesses. Although designers have learned to adapt their designs to materials of low ductility, there remains the desire to use high toughness materials. The toughness properties of intermetallic compounds and ceramics can be improved by embedding fibers within these materials to form a composite material.
In one approach to fabricating a composite article of reinforcing fibers in a matrix of an intermetallic compound or a ceramic, a layer of the matrix is first prepared. The reinforcing fiber or fibers are placed onto the matrix layer, and then another layer of the matrix is applied. These steps are repeated to gradually build up the layered composite article,
One of the problems that arises as the composite article is fabricated is that it is difficult to hold the fiber or fibers in the proper location as the succeeding layer of matrix material is applied. No satisfactory technique has been developed, because tile fiber or fibers cannot be easily attached to the underlying layer of low-ductility matrix material,
There therefore exists a need for an improved technique for fabricating composite materials by the layered buildup approach. Such a technique should permit the fabrication of composite materials having matrices of intermetallic compounds or ceramics of relatively low ductility. The present invention fulfills this need, and further provides related advantages.